From: Dipankar Sarma Use abstracted RCU API to dereference RCU protected data. Hides barrier details. Patch from Paul McKenney. This patch introduced an rcu_dereference() macro that replaces most uses of smp_read_barrier_depends(). The new macro has the advantage of explicitly documenting which pointers are protected by RCU -- in contrast, it is sometimes difficult to figure out which pointer is being protected by a given smp_read_barrier_depends() call. Signed-off-by: Paul McKenney Signed-off-by: Andrew Morton --- 25-akpm/arch/x86_64/kernel/mce.c | 8 +++----- 25-akpm/fs/dcache.c | 10 ++++------ 25-akpm/include/linux/list.h | 27 ++++++++++++++------------- 25-akpm/include/linux/rcupdate.h | 16 ++++++++++++++++ 25-akpm/ipc/util.c | 11 +++++------ 25-akpm/net/bridge/br_input.c | 3 +-- 25-akpm/net/core/dev.c | 3 +-- 25-akpm/net/core/netfilter.c | 3 +-- 25-akpm/net/decnet/dn_route.c | 17 ++++++++--------- 25-akpm/net/ipv4/icmp.c | 3 +-- 25-akpm/net/ipv4/ip_input.c | 3 +-- 25-akpm/net/ipv4/route.c | 24 ++++++++++-------------- 25-akpm/net/ipv6/icmp.c | 3 +-- 25-akpm/net/ipv6/ip6_input.c | 3 +-- 14 files changed, 67 insertions(+), 67 deletions(-) diff -puN arch/x86_64/kernel/mce.c~rcu-abstracted-rcu-dereferencing arch/x86_64/kernel/mce.c --- 25/arch/x86_64/kernel/mce.c~rcu-abstracted-rcu-dereferencing Fri Aug 6 15:14:09 2004 +++ 25-akpm/arch/x86_64/kernel/mce.c Fri Aug 6 15:14:09 2004 @@ -49,8 +49,7 @@ static void mce_log(struct mce *mce) mce->finished = 0; smp_wmb(); for (;;) { - entry = mcelog.next; - read_barrier_depends(); + entry = rcu_dereference(mcelog.next); /* When the buffer fills up discard new entries. Assume that the earlier errors are the more interesting. */ if (entry >= MCE_LOG_LEN) { @@ -340,9 +339,8 @@ static ssize_t mce_read(struct file *fil int i, err; down(&mce_read_sem); - next = mcelog.next; - read_barrier_depends(); - + next = rcu_dereference(mcelog.next); + /* Only supports full reads right now */ if (*off != 0 || usize < MCE_LOG_LEN*sizeof(struct mce)) { up(&mce_read_sem); diff -puN fs/dcache.c~rcu-abstracted-rcu-dereferencing fs/dcache.c --- 25/fs/dcache.c~rcu-abstracted-rcu-dereferencing Fri Aug 6 15:14:09 2004 +++ 25-akpm/fs/dcache.c Fri Aug 6 15:14:09 2004 @@ -620,7 +620,7 @@ void shrink_dcache_parent(struct dentry * * Prune the dentries that are anonymous * - * parsing d_hash list does not read_barrier_depends() as it + * parsing d_hash list does not hlist_for_each_rcu() as it * done under dcache_lock. * */ @@ -977,11 +977,10 @@ struct dentry * __d_lookup(struct dentry rcu_read_lock(); - hlist_for_each (node, head) { + hlist_for_each_rcu(node, head) { struct dentry *dentry; struct qstr *qstr; - smp_read_barrier_depends(); dentry = hlist_entry(node, struct dentry, d_hash); smp_rmb(); @@ -1008,8 +1007,7 @@ struct dentry * __d_lookup(struct dentry if (dentry->d_parent != parent) goto next; - qstr = &dentry->d_name; - smp_read_barrier_depends(); + qstr = rcu_dereference(&dentry->d_name); if (parent->d_op && parent->d_op->d_compare) { if (parent->d_op->d_compare(parent, qstr, name)) goto next; @@ -1062,7 +1060,7 @@ int d_validate(struct dentry *dentry, st spin_lock(&dcache_lock); base = d_hash(dparent, dentry->d_name.hash); hlist_for_each(lhp,base) { - /* read_barrier_depends() not required for d_hash list + /* hlist_for_each_rcu() not required for d_hash list * as it is parsed under dcache_lock */ if (dentry == hlist_entry(lhp, struct dentry, d_hash)) { diff -puN include/linux/list.h~rcu-abstracted-rcu-dereferencing include/linux/list.h --- 25/include/linux/list.h~rcu-abstracted-rcu-dereferencing Fri Aug 6 15:14:09 2004 +++ 25-akpm/include/linux/list.h Fri Aug 6 15:14:09 2004 @@ -423,11 +423,11 @@ static inline void list_splice_init(stru */ #define list_for_each_rcu(pos, head) \ for (pos = (head)->next, prefetch(pos->next); pos != (head); \ - pos = pos->next, ({ smp_read_barrier_depends(); 0;}), prefetch(pos->next)) + pos = rcu_dereference(pos->next), prefetch(pos->next)) #define __list_for_each_rcu(pos, head) \ for (pos = (head)->next; pos != (head); \ - pos = pos->next, ({ smp_read_barrier_depends(); 0;})) + pos = rcu_dereference(pos->next)) /** * list_for_each_safe_rcu - iterate over an rcu-protected list safe @@ -442,7 +442,7 @@ static inline void list_splice_init(stru */ #define list_for_each_safe_rcu(pos, n, head) \ for (pos = (head)->next, n = pos->next; pos != (head); \ - pos = n, ({ smp_read_barrier_depends(); 0;}), n = pos->next) + pos = rcu_dereference(n), n = pos->next) /** * list_for_each_entry_rcu - iterate over rcu list of given type @@ -458,8 +458,8 @@ static inline void list_splice_init(stru for (pos = list_entry((head)->next, typeof(*pos), member), \ prefetch(pos->member.next); \ &pos->member != (head); \ - pos = list_entry(pos->member.next, typeof(*pos), member), \ - ({ smp_read_barrier_depends(); 0;}), \ + pos = rcu_dereference(list_entry(pos->member.next, \ + typeof(*pos), member)), \ prefetch(pos->member.next)) @@ -475,7 +475,7 @@ static inline void list_splice_init(stru */ #define list_for_each_continue_rcu(pos, head) \ for ((pos) = (pos)->next, prefetch((pos)->next); (pos) != (head); \ - (pos) = (pos)->next, ({ smp_read_barrier_depends(); 0;}), prefetch((pos)->next)) + (pos) = rcu_dereference((pos)->next), prefetch((pos)->next)) /* * Double linked lists with a single pointer list head. @@ -581,12 +581,9 @@ static inline void hlist_add_head(struct * or hlist_del_rcu(), running on this same list. * However, it is perfectly legal to run concurrently with * the _rcu list-traversal primitives, such as - * hlist_for_each_entry(), but only if smp_read_barrier_depends() - * is used to prevent memory-consistency problems on Alpha CPUs. - * Regardless of the type of CPU, the list-traversal primitive - * must be guarded by rcu_read_lock(). - * - * OK, so why don't we have an hlist_for_each_entry_rcu()??? + * hlist_for_each_rcu(), used to prevent memory-consistency + * problems on Alpha CPUs. Regardless of the type of CPU, the + * list-traversal primitive must be guarded by rcu_read_lock(). */ static inline void hlist_add_head_rcu(struct hlist_node *n, struct hlist_head *h) @@ -631,6 +628,10 @@ static inline void hlist_add_after(struc for (pos = (head)->first; pos && ({ n = pos->next; 1; }); \ pos = n) +#define hlist_for_each_rcu(pos, head) \ + for ((pos) = (head)->first; pos && ({ prefetch((pos)->next); 1; }); \ + (pos) = rcu_dereference((pos)->next)) + /** * hlist_for_each_entry - iterate over list of given type * @tpos: the type * to use as a loop counter. @@ -696,7 +697,7 @@ static inline void hlist_add_after(struc for (pos = (head)->first; \ pos && ({ prefetch(pos->next); 1;}) && \ ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \ - pos = pos->next, ({ smp_read_barrier_depends(); 0; }) ) + pos = rcu_dereference(pos->next)) #else #warning "don't include kernel headers in userspace" diff -puN include/linux/rcupdate.h~rcu-abstracted-rcu-dereferencing include/linux/rcupdate.h --- 25/include/linux/rcupdate.h~rcu-abstracted-rcu-dereferencing Fri Aug 6 15:14:09 2004 +++ 25-akpm/include/linux/rcupdate.h Fri Aug 6 15:14:09 2004 @@ -222,6 +222,22 @@ static inline int rcu_pending(int cpu) */ #define rcu_read_unlock_bh() local_bh_enable() +/** + * rcu_dereference - fetch an RCU-protected pointer in an + * RCU read-side critical section. This pointer may later + * be safely dereferenced. + * + * Inserts memory barriers on architectures that require them + * (currently only the Alpha), and, more importantly, documents + * exactly which pointers are protected by RCU. + */ + +#define rcu_dereference(p) ({ \ + typeof(p) _________p1 = p; \ + smp_read_barrier_depends(); \ + (_________p1); \ + }) + extern void rcu_init(void); extern void rcu_check_callbacks(int cpu, int user); extern void rcu_restart_cpu(int cpu); diff -puN ipc/util.c~rcu-abstracted-rcu-dereferencing ipc/util.c --- 25/ipc/util.c~rcu-abstracted-rcu-dereferencing Fri Aug 6 15:14:09 2004 +++ 25-akpm/ipc/util.c Fri Aug 6 15:14:09 2004 @@ -100,7 +100,7 @@ int ipc_findkey(struct ipc_ids* ids, key int max_id = ids->max_id; /* - * read_barrier_depends is not needed here + * rcu_dereference() is not needed here * since ipc_ids.sem is held */ for (id = 0; id <= max_id; id++) { @@ -171,7 +171,7 @@ int ipc_addid(struct ipc_ids* ids, struc size = grow_ary(ids,size); /* - * read_barrier_depends() is not needed here since + * rcu_dereference()() is not needed here since * ipc_ids.sem is held */ for (id = 0; id < size; id++) { @@ -220,7 +220,7 @@ struct kern_ipc_perm* ipc_rmid(struct ip BUG(); /* - * do not need a read_barrier_depends() here to force ordering + * do not need a rcu_dereference()() here to force ordering * on Alpha, since the ipc_ids.sem is held. */ p = ids->entries[lid].p; @@ -515,13 +515,12 @@ struct kern_ipc_perm* ipc_lock(struct ip * Note: The following two read barriers are corresponding * to the two write barriers in grow_ary(). They guarantee * the writes are seen in the same order on the read side. - * smp_rmb() has effect on all CPUs. read_barrier_depends() + * smp_rmb() has effect on all CPUs. rcu_dereference() * is used if there are data dependency between two reads, and * has effect only on Alpha. */ smp_rmb(); /* prevent indexing old array with new size */ - entries = ids->entries; - read_barrier_depends(); /*prevent seeing new array unitialized */ + entries = rcu_dereference(ids->entries); out = entries[lid].p; if(out == NULL) { rcu_read_unlock(); diff -puN net/bridge/br_input.c~rcu-abstracted-rcu-dereferencing net/bridge/br_input.c --- 25/net/bridge/br_input.c~rcu-abstracted-rcu-dereferencing Fri Aug 6 15:14:09 2004 +++ 25-akpm/net/bridge/br_input.c Fri Aug 6 15:14:09 2004 @@ -56,8 +56,7 @@ int br_handle_frame_finish(struct sk_buf dest = skb->mac.ethernet->h_dest; rcu_read_lock(); - p = skb->dev->br_port; - smp_read_barrier_depends(); + p = rcu_dereference(skb->dev->br_port); if (p == NULL || p->state == BR_STATE_DISABLED) { kfree_skb(skb); diff -puN net/core/dev.c~rcu-abstracted-rcu-dereferencing net/core/dev.c --- 25/net/core/dev.c~rcu-abstracted-rcu-dereferencing Fri Aug 6 15:14:09 2004 +++ 25-akpm/net/core/dev.c Fri Aug 6 15:14:09 2004 @@ -1332,8 +1332,7 @@ int dev_queue_xmit(struct sk_buff *skb) * also serializes access to the device queue. */ - q = dev->qdisc; - smp_read_barrier_depends(); + q = rcu_dereference(dev->qdisc); #ifdef CONFIG_NET_CLS_ACT skb->tc_verd = SET_TC_AT(skb->tc_verd,AT_EGRESS); #endif diff -puN net/core/netfilter.c~rcu-abstracted-rcu-dereferencing net/core/netfilter.c --- 25/net/core/netfilter.c~rcu-abstracted-rcu-dereferencing Fri Aug 6 15:14:09 2004 +++ 25-akpm/net/core/netfilter.c Fri Aug 6 15:14:09 2004 @@ -783,13 +783,12 @@ void nf_log_packet(int pf, nf_logfn *logfn; rcu_read_lock(); - logfn = nf_logging[pf]; + logfn = rcu_dereference(nf_logging[pf]); if (logfn) { va_start(args, fmt); vsnprintf(prefix, sizeof(prefix), fmt, args); va_end(args); /* We must read logging before nf_logfn[pf] */ - smp_read_barrier_depends(); logfn(hooknum, skb, in, out, prefix); } else if (!reported) { printk(KERN_WARNING "nf_log_packet: can\'t log yet, " diff -puN net/decnet/dn_route.c~rcu-abstracted-rcu-dereferencing net/decnet/dn_route.c --- 25/net/decnet/dn_route.c~rcu-abstracted-rcu-dereferencing Fri Aug 6 15:14:09 2004 +++ 25-akpm/net/decnet/dn_route.c Fri Aug 6 15:14:09 2004 @@ -1,4 +1,3 @@ - /* * DECnet An implementation of the DECnet protocol suite for the LINUX * operating system. DECnet is implemented using the BSD Socket @@ -1175,8 +1174,8 @@ static int __dn_route_output_key(struct if (!(flags & MSG_TRYHARD)) { rcu_read_lock_bh(); - for(rt = dn_rt_hash_table[hash].chain; rt; rt = rt->u.rt_next) { - smp_read_barrier_depends(); + for(rt = rcu_dereference(dn_rt_hash_table[hash].chain); rt; + rt = rcu_dereference(rt->u.rt_next)) { if ((flp->fld_dst == rt->fl.fld_dst) && (flp->fld_src == rt->fl.fld_src) && #ifdef CONFIG_DECNET_ROUTE_FWMARK @@ -1454,8 +1453,8 @@ int dn_route_input(struct sk_buff *skb) return 0; rcu_read_lock(); - for(rt = dn_rt_hash_table[hash].chain; rt != NULL; rt = rt->u.rt_next) { - read_barrier_depends(); + for(rt = rcu_dereference(dn_rt_hash_table[hash].chain); rt != NULL; + rt = rcu_dereference(rt->u.rt_next)) { if ((rt->fl.fld_src == cb->src) && (rt->fl.fld_dst == cb->dst) && (rt->fl.oif == 0) && @@ -1648,8 +1647,9 @@ int dn_cache_dump(struct sk_buff *skb, s if (h > s_h) s_idx = 0; rcu_read_lock_bh(); - for(rt = dn_rt_hash_table[h].chain, idx = 0; rt; rt = rt->u.rt_next, idx++) { - smp_read_barrier_depends(); + for(rt = rcu_dereference(dn_rt_hash_table[h].chain), idx = 0; + rt; + rt = rcu_dereference(rt->u.rt_next), idx++) { if (idx < s_idx) continue; skb->dst = dst_clone(&rt->u.dst); @@ -1692,9 +1692,8 @@ static struct dn_route *dn_rt_cache_get_ static struct dn_route *dn_rt_cache_get_next(struct seq_file *seq, struct dn_route *rt) { - struct dn_rt_cache_iter_state *s = seq->private; + struct dn_rt_cache_iter_state *s = rcu_dereference(seq->private); - smp_read_barrier_depends(); rt = rt->u.rt_next; while(!rt) { rcu_read_unlock_bh(); diff -puN net/ipv4/icmp.c~rcu-abstracted-rcu-dereferencing net/ipv4/icmp.c --- 25/net/ipv4/icmp.c~rcu-abstracted-rcu-dereferencing Fri Aug 6 15:14:09 2004 +++ 25-akpm/net/ipv4/icmp.c Fri Aug 6 15:14:09 2004 @@ -705,8 +705,7 @@ static void icmp_unreach(struct sk_buff read_unlock(&raw_v4_lock); rcu_read_lock(); - ipprot = inet_protos[hash]; - smp_read_barrier_depends(); + ipprot = rcu_dereference(inet_protos[hash]); if (ipprot && ipprot->err_handler) ipprot->err_handler(skb, info); rcu_read_unlock(); diff -puN net/ipv4/ip_input.c~rcu-abstracted-rcu-dereferencing net/ipv4/ip_input.c --- 25/net/ipv4/ip_input.c~rcu-abstracted-rcu-dereferencing Fri Aug 6 15:14:09 2004 +++ 25-akpm/net/ipv4/ip_input.c Fri Aug 6 15:14:09 2004 @@ -231,10 +231,9 @@ static inline int ip_local_deliver_finis if (raw_sk) raw_v4_input(skb, skb->nh.iph, hash); - if ((ipprot = inet_protos[hash]) != NULL) { + if ((ipprot = rcu_dereference(inet_protos[hash])) != NULL) { int ret; - smp_read_barrier_depends(); if (!ipprot->no_policy && !xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) { kfree_skb(skb); diff -puN net/ipv4/route.c~rcu-abstracted-rcu-dereferencing net/ipv4/route.c --- 25/net/ipv4/route.c~rcu-abstracted-rcu-dereferencing Fri Aug 6 15:14:09 2004 +++ 25-akpm/net/ipv4/route.c Fri Aug 6 15:14:09 2004 @@ -237,9 +237,8 @@ static struct rtable *rt_cache_get_first static struct rtable *rt_cache_get_next(struct seq_file *seq, struct rtable *r) { - struct rt_cache_iter_state *st = seq->private; + struct rt_cache_iter_state *st = rcu_dereference(seq->private); - smp_read_barrier_depends(); r = r->u.rt_next; while (!r) { rcu_read_unlock_bh(); @@ -1004,10 +1003,9 @@ void ip_rt_redirect(u32 old_gw, u32 dadd rthp=&rt_hash_table[hash].chain; rcu_read_lock(); - while ((rth = *rthp) != NULL) { + while ((rth = rcu_dereference(*rthp)) != NULL) { struct rtable *rt; - smp_read_barrier_depends(); if (rth->fl.fl4_dst != daddr || rth->fl.fl4_src != skeys[i] || rth->fl.fl4_tos != tos || @@ -1259,9 +1257,8 @@ unsigned short ip_rt_frag_needed(struct unsigned hash = rt_hash_code(daddr, skeys[i], tos); rcu_read_lock(); - for (rth = rt_hash_table[hash].chain; rth; - rth = rth->u.rt_next) { - smp_read_barrier_depends(); + for (rth = rcu_dereference(rt_hash_table[hash].chain); rth; + rth = rcu_dereference(rth->u.rt_next)) { if (rth->fl.fl4_dst == daddr && rth->fl.fl4_src == skeys[i] && rth->rt_dst == daddr && @@ -1864,8 +1861,8 @@ int ip_route_input(struct sk_buff *skb, hash = rt_hash_code(daddr, saddr ^ (iif << 5), tos); rcu_read_lock(); - for (rth = rt_hash_table[hash].chain; rth; rth = rth->u.rt_next) { - smp_read_barrier_depends(); + for (rth = rcu_dereference(rt_hash_table[hash].chain); rth; + rth = rcu_dereference(rth->u.rt_next)) { if (rth->fl.fl4_dst == daddr && rth->fl.fl4_src == saddr && rth->fl.iif == iif && @@ -2232,8 +2229,8 @@ int __ip_route_output_key(struct rtable hash = rt_hash_code(flp->fl4_dst, flp->fl4_src ^ (flp->oif << 5), flp->fl4_tos); rcu_read_lock_bh(); - for (rth = rt_hash_table[hash].chain; rth; rth = rth->u.rt_next) { - smp_read_barrier_depends(); + for (rth = rcu_dereference(rt_hash_table[hash].chain); rth; + rth = rcu_dereference(rth->u.rt_next)) { if (rth->fl.fl4_dst == flp->fl4_dst && rth->fl.fl4_src == flp->fl4_src && rth->fl.iif == 0 && @@ -2464,9 +2461,8 @@ int ip_rt_dump(struct sk_buff *skb, str if (h > s_h) s_idx = 0; rcu_read_lock_bh(); - for (rt = rt_hash_table[h].chain, idx = 0; rt; - rt = rt->u.rt_next, idx++) { - smp_read_barrier_depends(); + for (rt = rcu_dereference(rt_hash_table[h].chain), idx = 0; rt; + rt = rcu_dereference(rt->u.rt_next), idx++) { if (idx < s_idx) continue; skb->dst = dst_clone(&rt->u.dst); diff -puN net/ipv6/icmp.c~rcu-abstracted-rcu-dereferencing net/ipv6/icmp.c --- 25/net/ipv6/icmp.c~rcu-abstracted-rcu-dereferencing Fri Aug 6 15:14:09 2004 +++ 25-akpm/net/ipv6/icmp.c Fri Aug 6 15:14:09 2004 @@ -530,8 +530,7 @@ static void icmpv6_notify(struct sk_buff hash = nexthdr & (MAX_INET_PROTOS - 1); rcu_read_lock(); - ipprot = inet6_protos[hash]; - smp_read_barrier_depends(); + ipprot = rcu_dereference(inet6_protos[hash]); if (ipprot && ipprot->err_handler) ipprot->err_handler(skb, NULL, type, code, inner_offset, info); rcu_read_unlock(); diff -puN net/ipv6/ip6_input.c~rcu-abstracted-rcu-dereferencing net/ipv6/ip6_input.c --- 25/net/ipv6/ip6_input.c~rcu-abstracted-rcu-dereferencing Fri Aug 6 15:14:09 2004 +++ 25-akpm/net/ipv6/ip6_input.c Fri Aug 6 15:14:09 2004 @@ -167,10 +167,9 @@ resubmit: ipv6_raw_deliver(skb, nexthdr); hash = nexthdr & (MAX_INET_PROTOS - 1); - if ((ipprot = inet6_protos[hash]) != NULL) { + if ((ipprot = rcu_dereference(inet6_protos[hash])) != NULL) { int ret; - smp_read_barrier_depends(); if (ipprot->flags & INET6_PROTO_FINAL) { struct ipv6hdr *hdr; _